Stress is a killer and it sounds like you have a lot of it right now! Talk to your husband, change your routine and try to go to bed earlier (even if it means sacrificing your favorite TV programs). I had to tell my husband that if he ever wanted to "get lucky" again, we had to go to bed by 10 - normally I would go at 11 or 11:30. After having my daughter, bed time was just that, time to SLEEP!!!!! Also, talk to him about sharing the burden of care. It took both of you to create your son, it will take both of you to care for him (no matter what hour of the day). Let him know that you are on the verge of having a breakdown (OK - maybe a little melodramatic) and that you really need a lot more support from him right now, it's ok to say you can't handle everything, we don't need to be SuperMom.
Also, if you are on a hormonal BC, you might want to try changing brands or birth control methods. I was on depo provera after having my daughter and it really messed me up. I went off it on my own, but that didn't straighten my hormones back out, it wasn't until I went on the pill for a few months that I returned to "normal". When you come out of a depression, it's amazing to feel how much better the world is, and to realize how low you really felt - you'll still have all the stress and good days and bad days, but your coping mechanism will be so much better and you'll feel happiness and joy and it will feel "real". If you are not on any hormonal birth control and you don't feel better after your son gets through his teething and with getting your hubby to take on more of the workload, you may want to talk to someone about depression. Exhaustion definitely plays a huge part in it, but if you improve that as much as you can and you don't feel a change after a couple of weeks, you may need a little (probably temporary) help.
As far as the teething goes, my daughter's early teeth came in quickly and with no problems other than a constant stream of drool :) When it came to her molars, these hurt her, plus it gave her diarrhea and horrible diaper rash in addition to the teething pain. You will all get through it, but it may not be pleasant. Good luck!